A process controller typically operates by comparing values of a process variable with a target value to determine whether the process is operating within acceptable bounds. For example, in a process in which a water flow cools a power source, a controller monitors a temperature of the power source and, if necessary to prevent the power source from overheating, reduces the temperature of the water.
An adaptive controller is a controller that adjusts or adapts its parameters to suit the current process condition based on the behavior of the controller inputs and/or outputs. For adaptive control, a controller may identify a model of the process under control and generate new controller parameters from the identified process model. The process model may have a preselected number of parameters to identify. Process parameters may be determined by having the controller upset the process in an open-loop mode and measure the process response. One advantage of identifying a process model is that the model enables direct calculation of the controller tuning parameters, avoiding the need for a slowly converging performance feedback method.
A valve positioner system is a position controller that controls the position of a valve in response to a set point signal. For example, in a chemical mixing process, a valve positioner system may be used to regulate flow which would then change a concentration of a particular chemical in the mixing process. A chemical mixing process controller monitors the concentrations of all chemicals in the mix and provides set point signals to various valve positioners which vary the flow of the chemicals.
A valve positioner system controls position of the valve by comparing a measured position with a set point or target position and changing its output accordingly. The valve positioner system typically includes a current-to-pressure (i/p) transducer that receives a variable electrical input signal and provides a pneumatic output signal. The valve positioner system employs the i/p transducer in a feedback loop that includes a pneumatic relay, a valve actuator, a valve having a valve stem attached to a valve flow modulating member, a positioner feedback linkage, a position sensor, and a microprocessor.
The microprocessor receives the set point signal and produces the input signal for the i/p transducer. The valve actuator responds to the pressure change produced by the pneumatic relay by driving the valve stem to control the degree to which the valve is open. The positioner feedback linkage transmits the position of the valve stem to the position sensor, which provides a signal indicative of the position to the microprocessor. The microprocessor then adjusts the signal supplied to the i/p transducer so as to move the valve to the position indicated by the set point, or to maintain the position of the valve at the set point.